Ammonium alum



Patented Apr, 16, 1929.

CHARLES MCCOMBIE BROWN OF TORONTO, ONTARIO, CANADA.

AMMoNIUivi- ALUM.

No Drawing.

My invention relates to a process for manufacturii'ig ammonium alum by a furnace or retort treatment of materials containing aluminum such as oxides, alunite, Chappell residues, etc. in which, more or less iron is present with acid sulphate of ammonia. A process of this kind is described in my application for patent Serial No. 750,498 filed Nov. 17, 1924. In that process the aluminum containing compound and the reagent are mixed together and then heated to a temperature sufficiently high to form the ammonium alum and to substantially convert any soluble iron compounds formed into insoluble compounds. In said process soluble iron compounds are unavoidably formed in heating up the mixture at temperatures below the maximum to which the material is ultimately subjected but are mainly decomposed at the higher temperatures finally reached.

I have found that better results in some respect-s are obtained by preventing the formation of the soluble iron compounds altogether and this I accomplish by avoiding the temperatures of formation of iron compounds during the period in which the alummum containing material and the acid ammonium sulphate are in chemical contact with each other.

.With this in view I heat the aluminum containing material out of contact with the sulphate to a temperature above that at which soluble iron compounds will form and at which it will contain sufficient heat so that when mixed with the acid ammonium sulphate the mixture will be at a temperature above that at which the soluble iron compounds will form and thereafter, until the reaction is finished, supply suflicient heat to the mixture to maintain such temperature. The temperature to which the aluminum bearing material must be raised, of course depends upon the cooling influences to which it is subjected when admixed or in contact with the acid ammonium sulphate and on the temperature of the latter. Thus, if the sulphate is preheated and the furnace temperature to which the mixture is subjected is relatively high, the temperature to which the aluminum bearing material is raised need not be so high as would otherwise be the case. Preferably the acid ammonium sulphate is stantially equal to or above that at which the reaction is to take place. Preferably,

Application filed October 14, 1925.

preheated to a temperature sub- Serial No. 62467.

the aluminous material should be heated to 800 degrees'F. or more and I have found 850 or higher to be most satisfactory. Temperatures somewhat lower than 800 F. may be used to some advantage, particularly if the acid ammonium sulphate is preheated as indicated above, but in any event the aluminous material should be hot enough to avoid any drop of the mixture to a temperature at which the soluble iron salts would form. I have found that soluble iron salts will not form to any considerable extent above 750 F.

lVhen the acid ammonium sulphate is heat-- ed approximately to the reacting temperature it becomes liquid and it is convenient to preheat it sufliciently high to liquefy it and feed it to the aluminum compounds in this condition. So far as I now know, and it appears to be the fact, the acid ammonium sulphate combines with the aluminum if the latter is in the form of the oxide, as is mainly the case in the above mentioned compounds according to the following equation:

These specific proportions of aluminum bearing material to reagent are not important as it is found that if the former is in excess the amount of alum formed depends upon the amount of sulphate present, and, irrespective of the proportion of reagent to the aluminum bearing material, no other substance is formed in material quantities but the ammonium alum, the residues after the separation of the alum, being substantially the same as the original aluminum bearing material. As an example of a successful practice, however, I may mention an instance of the practice of my invention in which 100 parts of aluminum in the form of a dehydrated oxide were mixed after preheating with about 400 parts of acid ammonium sulphate.

' The material after leached with water and the ammonium alum separated therefrom in the well known manner by crystallization, any iron therein practically all remaining with the insoluble residues. The residues, if they contain suflicient aluminum to warrant, may be retreated.

My invention is entirely independent of the apparatus in which it is carried out. It might well be carried out in one of the furnacing may be common forms of retorts, as, for example, in

which consists in heating the aluminum bearing material to a vtemperature at which sulphuric acid salts of iron are unstable, melting acid ammonium sulphate, bringing the alum bearing material and'the sulphate into chemical contact and supplying sulficient heat to prevent the temperature dropping to a point at which soluble iron salts are formed during the reaction.

CHARLES MGGOMBIE BROWN. 

